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I was told by A/C guy I have a short somewhere to the high pressure switch. something is not kicking on the compressor. another mechanic said I need a new computer. what do you think

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Go with the ac guy
there are systems that prevent the ac compressor working
high pressure switch which cuts the ac clutch if the head pressure goes too high
low pressure switch which cuts power to the ac compressor if there
is no gas in the system
climate control systems which cut power when the ac is not required
fuses to the ac system
get a better explanation or seek advice from other ac mechanics

Posted on May 02, 2015

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Posted on Jan 02, 2017

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A/C Compressor won't turn on Can jump compressor from battery and compressor comes on & cools. Hi pressure switch checks out ok and 12 volts going to hi pressure switch no voltage to compressor


the high pressure switch kicks the compressor off when the pressure rises, the low pressure switch kicks it on, check that switch, unplug the wire and use a continuity meter to see if the switch functions, also check for power getting to the plug itself

Sep 25, 2011 | 2002 Chevrolet Blazer

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The ac compressor kicks on and off. We have had a professional look at it, but they couldn't find a problem. However, the compressor doesn't run long enough to get the air cold. Is this an...


Could be either. Usually if the compressor is cycling than its usually low on refrigerant. Could be pressure sensor. Could be cooling fan. I would have a different tech look at it. It is hard to diagnose what is going on without knowing pressures of the high and low side from a gage hooked up to the system.

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1 Answer

My 2004 chevy 1500 v8 air compressor will not kick in. I have jumped the low pressure switch and the compressor will not come on. i have changed the temperature controller and still won't kick in. i...


If the compressor kick's in when you jumper the relay socket there is no problem with the electrical to the compressor an the compressor isn't locked up . You have a control side problem , the PCM - engine computer is suppose to energize the relay if no other problems are present . The proper way to check this would be to hook up a scan tool an check pressure input's to the PCM an is the PCM getting a request from the HVAC control panel to turn on the A/C compressor . AutoZone is wrong as usual , There can be codes without the check engine light being on . o'reilly's is wrong as well DTC P0530 (LU3, LR4, LM7, LQ4 and L18)
The powertrain control module (PCM) or engine control module (ECM) monitors the high side refrigerant pressure via a A/C refrigerant pressure sensor. When the pressure is high the signal voltage is high. When the pressure is low the signal voltage is low. When pressure is too high the PCM will not allow the A/C compressor clutch to engage.

Action Taken When the DTC Sets
The malfunction indicator lamp (MIL) will not illuminate.
Diagnostic Aids
The air conditioning (A/C) compressor clutch will not engage under the following conditions:
• The A/C high side line pressure is over 2957 kPa (429 psi).
• The A/C low side line pressure is under 138-172 kPa (20-25 psi).
• Throttle angle is at 100 percent.
• Engine speed is more than 5500 RPM.
• Engine coolant temperature (ECT) is more than 121°C (250°F).
• Ambient air temperature is less than 5°C (40°F).
• Engine is idling at a low unstable RPM
Compressor clutch engagement cannot be used to determine status of the low pressure switch. The low pressure switch is one of several inputs to the HVAC control module for A/C request authorization. A/C request is one of several inputs to the powertrain control module (PCM) that control A/C compressor clutch engagement.
To accurately determine what pressure the A/C low pressure switch opens and closes at use Kent Moore GE-47742 which will allow the technician to measure the switch point pressure at the switch.
Using a scan tool, monitor the "low pressure switch" status while monitoring the "low side" pressure at the switch to determine the switch points of the low pressure switch.
The low pressure switch "connector seal" must be removed before plugging it into the switch for testing. The "plunger effect" of plugging the connector with seal into the switch induces a pressure on the back side of the switch, this pressure will skew the opening/closing characteristics of the switch 5-10 psi until the pressure bleeds off. The time required for the connection induced pressure to bleed off can take 20 minutes or longer

Do you have the proper diagnostic tools ? Factory scan tool , A/C gauges ? You best bet , take your vehicle to a qualified repair shop !!

Apr 11, 2017 | 1996 Chevrolet Tahoe

1 Answer

After replacing a high pressure switch on my 98 gmc sierra a/c


Take your truck somewhere else... "wouldn't take charge" doesn't even make any sense... The A/c system on any vehicle has 2 switches, high pressure, which is a "fan request/safety" switch that turns off the compressor clutch and turns on the engine fan in electric fan applications when refrigerant pressure reaches around 300 PSI to drop the pressure and complete the refrigeration cycle, and the low pressure switch, which basically doesn't allow the compressor clutch to run if the system is low/empty of refrigerant (turns it off under about 10-20 PSI). My guess is, if he couldn't get the refrigerant back in the system, either his a/c service machine was malfunctioning, or he didn't know how to use it... I've seen a LOT of both on the field... I'm sorry to say there is a lot of people working on automotive A/c out there that don't really know what they're doing, but sincerely believe they do... Short of giving you a definite answer, i'd get a second opinion on that before spending any good money on a compressor (which are usually pretty pricey)

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My airconditioner is blowing hot air. The mechanic said that the compressor is not broken. He needed to find the lower side pressure valve to kick the compressor on so it would stay on. Where is the valve?


If it is the 3.5 litre it has a triple switch located on the top of the dryer that switch is actually the high pressure switch the low pressure switch and medium when the pressure is medium or you jump it than fans will kick on high he is right about the thermistor for the evaporator he should just apply 12volts to the compressor to see if the coil on the compressor is bad all three are common problems not knowing where the switch is makes me wonder if he even checked the relay or how he knows the compressor isnt bad

Jul 01, 2009 | 2003 Kia Sedona

1 Answer

Dodge Ram AC not blowing cold


By pass both pressure switches one at a time with small wire or a paper clip. If comperssor kicks on replace the swich that you bypassed.
if not it could be the fan clutch ot the compressor. Compressor runs about $400.00

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1 Answer

I have a 96 lumina 3.1 car. the ac compressor will work fine sometimes, and other times it will not kick on. it is full of freon......?someone said the low pressure switch could be bad. i cannot find that...


Compressor clutches go bad sometimes.. it is an electromagnetic device on front of compressor. You may also need shot of refrigerant. Level may be at point where it is on brink of being low.

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1 Answer

Air conditioners not working just blowing hot air . when u turn it on , u can hear that it want to start, but shortly after it shut down


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Jul 02, 2008 | 2001 Mitsubishi Montero

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